1. Field of the Invention
The present invention relates to a dielectric filter in which a resonator is formed on a dielectric plate, a transmission/reception sharing device and a communication device using the dielectric filter.
2. Description of the Related Art
A bandpass filter having a plurality of resonators in series has been used in a communication device.
To obtain large attenuation above and below a pass band, the so called xe2x80x9cjump-coupling methodxe2x80x9d has been utilized. In accordance with the method, a pair of resonators are directly electromagnetically coupled to each other jumping over another resonator therebetween. By causing the jump-coupling, a notch or pole appears outside the pass band
On the other hand, a planar-circuit type dielectric filter is expected to be widely used in a wireless LAN, a portable visual telephone and a next generation satellite broadcasting system. These applications use sub-millimeter waves. This type of filter is described in Japanese Patent Application No. 9-103017. It should be noted that the Japanese application was not laid-open to the public at the time of filing Japanese Patent Application No. 10-171174 on which this case is based. Thus, the reference is provided as background information to show the state of the art only. The citation of the reference is not to be construed as an admission that it constitutes prior art.
The application No. JP-A-9-103017 discloses a dielectric filter in which an electrode is formed on each side of a dielectric plate to constitute a resonator at the prescribed position of the dielectric plate, a micro-strip line is formed on a substrate, and the micro-strip line is coupled with the dielectric resonator.
This dielectric filter is extremely advantageous, being compact in size, easy to manufacture, and capable of easily obtaining the desired characteristics.
The above-mentioned jump-coupling is also effective to secure the large attenuation on the high-frequency side or the low-frequency side of its pass band of the planar circuit type dielectric filter.
An example is illustrated in FIG. 19 and FIG. 20, where the above-mentioned filter device in which a part of the dielectric plate is used as the resonator and a structure for causing jump-coupling between the resonators is implemented. FIG. 19 is an assembly view in which electrodes 2, 3 having electrode-free parts of the same shape opposite to each other across a dielectric plate are provided on each side of the dielectric plate 1 to constitute a third-order filter. Numerals 4a, 4b and 4c denote electrode-free parts on the upper surface thereof. Numeral 6 denotes a substrate on which a microstrip line to be coupled with the resonator is formed, and a basic part of the dielectric filter is constituted by successively laminating a package 8, the dielectric plate 1, an electromagnetic wave absorption body 11 and a shield 12 comprising a metallic plate thereon. In order to cause a pole outside the pass band, a semi-rigid cable in which a coupling loop is formed on each end is provided on the shield 12 in order to cause jump-coupling between a first-stage resonator and a third-stage resonator as illustrated in the figures.
FIG. 20 illustrates a sectional view of the abovementioned dielectric filter. The filter device has a higher profile because of the diameter of the semi-rigid cable. Thus, a dead space may be produced when the filter device is installed in electronic equipment. Also, a separate semi-rigid cable is necessary, the assembly process requires machining and soldering to form the coupling loop, and the cost is increased as a whole. Further, because the position of an attenuation pole is largely changed depending on the direction, length, etc., of the coupling loop, it is relatively difficult to adjust the position of the cable to obtain a desired filter characteristic.
The present invention provides a dielectric filter in which the above-mentioned problems caused by using separate parts such as a semi-rigid cable are solved, and a transmission/reception sharing device and communication device using the dielectric filter.
In the present invention, an electrode having electrode-free parts opposite to each other, on opposite sides of a dielectric plate, is provided on each side of the dielectric plate, an area between the electrode electrode-free parts is a resonator, and a plurality of stages of resonators in which adjacent resonators are successively coupled with each other, are provided on the dielectric plate. A coupling line for polarization, which directly couples two resonators by respectively coupling the line with the two resonators which may be separated from each other by one or more other stages among a plurality of resonators, is provided on a substrate separated from the dielectric plate by a prescribed distance. In such a structure, the coupling line for polarization is provided on the substrate, and no parts such as the semi-rigid cable are projected outside, and the device is not increased in size.
In the present invention, a line for signal input/output to be coupled with prescribed resonators is provided on the substrate provided with the coupling line for causing a pole. This structure dispenses with a special substrate on which a coupling line for causing a pole is provided in addition to a substrate on which the line for signal input/output is provided.
The substrate provided with the coupling line is used as a shield cover by forming an electrode on approximately the whole surface opposite to a surface on which the coupling line for polarization is formed. The structure dispenses with a single shield cover, and also dispenses with a substrate exclusively used for forming the coupling line for polarization.
In the present invention, an electrode having openings of approximately same shape which are opposite to each other, on opposite sides of a dielectric plate, is provided on each side of the dielectric plate, an area between the openings is a resonator, and a plurality of stages of resonators in which adjacent resonators are successively coupled with each other, are provided on the dielectric plate. A coupling line for polarization, which directly couples two resonators, e.g., through a slot line, by respectively coupling the line with the two resonators which may be separated from each other by one or more other stages among a plurality of resonators, is provided on the substrate. Such a structure dispenses with a substrate for forming the coupling line for polarization, and simultaneous patterning is realized in forming resonators.
Also, in the present invention, a transmission/reception sharing device is constituted by providing either of the above-mentioned dielectric filters as a transmission filter, a reception filter, or both filters.